It is known to make a power supply redundant in a server device or the like in case of, for example, a failure of a power supply unit. As a technique to make a power supply redundant, for example, techniques described in Patent Documents 1 to 3 are known.
Patent Document 1 describes a storage device (a server device) which has two AC/DC (Alternating Current/Direct Current) power supply parts (power supply units) connected to different power supply paths, respectively. By thus equipping a storage device with a plurality of AC/DC power supply parts and making a power supply path redundant, it is possible to, even if a failure occurs on one of the paths, supply electric power via the other path that is normal. As a result, the storage device can normally run even if a failure occurs on one of the power supply paths, for example, one of the AC/DC power supply parts.
Further, Patent Document 2 describes an information processing system which has an external power supply device and a plurality of system devices (server devices) supplied with DC power by the external power supply device. According to Patent Document 2, the external power supply device has a plurality of power supply modules each including an AC/DC converter converting an AC power input to a DC power input, a battery outputting DC, and a unit to select and output either a DC output by the AC/DC converter or a DC output by the battery. Moreover, in the case described in Patent Document 2, for example, n+1 pieces of power supply modules are provided for n pieces of system devices. According to Patent Document 2, by thus making a power supply module redundant, it is possible to, even if a failure occurs in any of the power supply modules, replace the power supply module and return to the original status without stopping the system device.
Patent Document 1: Japanese Unexamined Patent Application Publication No. JP-A 2007-280554
Patent Document 2: Japanese Unexamined Patent Application Publication No. JP-A 2003-264939
In a case where one server device has two AC/DC power supply parts as described in Patent Document 1, power supply devices (AC/DC power supply parts) twice as many as a server device are needed. However, it is quite rare that a plurality of power supply devices simultaneously break down in a server device in a rack, and it seems to be very useless in view of space, price and heat cooling to prepare a spare power supply device for each server in case of such a rare case. Thus, there is a problem of much waste in view of cost and so on in equipping one server device with two AC/DC power supply parts.
Further, in a case where a server device is configured to be supplied with power only from an external power supply device as described in Patent Document 2, the server device cannot be used alone. Therefore, use of the configuration of Patent Document 2 has a problem of lack of versatility.
As mentioned above, the techniques described in Patent Documents 1 and 2 have problems such as much waste and lack of versatility. Thus, a server device or the like has a problem of difficulty to employ a redundant power supply configuration which is economical, versatile and appropriate.